Porth's Essentials of Pathophysiology, 4e

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Circulatory Function

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AdvancedTherapies Individuals with heart failure are at significant risk of sudden cardiac death from ventricular fibrillation or ventricular tachycardia. Implantation of a cardioverter– defibrillator is indicated in selected patients with heart failure to prevent sudden cardiac death. 1,2 A cardioverter– defibrillator is a programmable implanted device that monitors the cardiac rhythm. It has the capacity to pace the heart and deliver electric shocks to terminate lethal arrhythmias. Refractory heart failure reflects deterioration in cardiac function that is unresponsive to medical or surgical inter- ventions. Since the early 1960s, significant progress has been made in improving the efficacy of ventricular assist devices (VADs), which are mechanical pumps used to support ventricular function. 41 VADs are used to decrease the workload of the myocardium while maintaining car- diac output and systemic arterial pressure. This decreases the workload on the ventricle and allows it to rest and recover. Most VADs require an invasive open chest pro- cedure for implantation. They may be used in patients who fail or have difficulty being weaned from cardiopul- monary bypass after cardiac surgery, those who develop cardiogenic shock after myocardial infarction, those with end-stage cardiomyopathy, and those who are awaiting cardiac transplantation. Earlier and more aggressive use of VADs as a bridge to transplantation and destination ther- apy (permanent support) has been shown to increase sur- vival. 41,42 Ventricular assist devices that allow the patient to be mobile and managed at home are sometimes used for long-term or permanent support for treatment of end-stage heart failure, rather than simply as a bridge to transplanta- tion. Ventricular assist devices can be used to support the function of the left ventricle, right ventricle, or both. 42 Heart transplantation is the preferred treatment for many persons with end-stage cardiac failure and oth- erwise good life expectancy. 1,2 Despite the overall suc- cess of heart transplantation, donor availability remains a key problem, and thousands are denied transplanta- tion each year. Left ventricular remodeling is a surgi- cal procedure designed to restore the size and shape of the ventricle, and in a subset of patients with severe left ventricular dysfunction this procedure may provide an alternative to cardiac transplantation. 43  Heart Failure in the Elderly Heart failure is one of the most common causes of dis- ability in the elderly and is the most frequent hospital discharge diagnosis for the elderly. Among the factors that have contributed to the increased numbers of older people with heart failure are the improved therapies for ischemic and hypertensive heart disease. 44 Thus, persons who would have died from acute myocardial disease 20 years ago are now surviving, but with residual heart damage. Advances in treatment of other diseases have also contributed indirectly to the rising prevalence of heart failure in the older population. In contrast to the etiology in middle-aged persons with heart failure,

the kidneys. Angiotensin-converting enzyme inhibitors have been shown to limit these harmful complications. The angiotensin II receptor blockers appear to have similar but more limited beneficial effects. They have the advantage of not causing a cough, which is a trouble- some side effect of the ACE inhibitors for many persons. Aldosterone receptor antagonists may be used in combi- nation with other agents for persons with heart failure. Hyperkalemia is a potential side effect of aldosterone antagonism that requires additional monitoring. 1 β -Adrenergic receptor blocking drugs are used to decrease left ventricular dysfunction associated with activation of the sympathetic nervous system. 40 Large clinical trials have shown that long-term therapy with β -adrenergic receptor blocking agents reduces morbid- ity and mortality in persons with chronic heart failure. The mechanism of this benefit remains unclear, but it is likely that chronic elevation of catecholamines and sympathetic nervous system activity causes progressive myocardial damage, leading to a worsening of left ven- tricular function and a poorer prognosis in persons with heart failure. Digitalis has been a recognized treatment for heart failure for over 200 years. The various forms of digi- talis are called cardiac glycosides. They improve cardiac function by increasing the force and strength of ventricu- lar contractions. Digitalis and related cardiac glycosides are inotropic agents that exert their effects by inhibiting the Na + /K + -ATPase membrane pump, which increases intracellular sodium; this in turn leads to an increase in intracellular calcium through the Na + /Ca + exchange pump 40 (see Fig. 20-1). The cardiac glycosides also decrease sinoatrial node activity and decrease conduc- tion through the atrioventricular node, thereby slowing the heart rate and increasing diastolic filling time. Vasodilator agents such as isosorbide dinitrate and hydralazine may be added to other standard medica- tions for African-American patients with chronic heart failure. 1 Agents such as nitroglycerin, nitroprusside, and nesiritide (B-type natriuretic peptide) are used in AHFSs to improve left heart performance by decreasing the pre- load (through vasodilation) or reducing the afterload (through arteriolar dilation), or both. OxygenTherapy Oxygen therapy increases the oxygen content of the blood and is often used in patients with acute episodes of heart failure. Noninvasive ventilation using continu- ous positive airway pressure (CPAP) may be used to relieve dyspnea, respiratory distress, and/or pulmonary edema. 34 Continuous positive airway pressure by face mask reduces the need for endotracheal intubation and has minimal adverse effects or complications. Because CPAP increases intrathoracic pressure, it also has the potential for decreasing venous return and left ventricular preload, thereby improving the cardiac ejection fraction and stabilizing the hemodynamic status in persons with severe heart failure. 40 Noninvasive ventilation can also be provided by bilevel ventilation (BiPAP), which delivers positive pressure during both inspiration and expiration.